1. Field of the Invention
The present invention relates to a semiconductor material, a production method thereof and a semiconductor device and, in particular, to a silicon carbide-based semiconductor material favorably used for production of devices having a step-terrace structure such as quantum wire devices, optical devices and electronic devices, a semiconductor device using the same, and a method of producing the semiconductor material.
2. Description of the Related Art
Various semiconductor materials other than silicon have been studied with a view to improvements in mobility and performance of semiconductor devices. Silicon carbide (SiC), a semiconductor material having a larger band gap than silicon, has in recent years shown promise in terms of application to power devices, high-frequency devices, and the like.
For a silicon carbide substrate, a 4H—SiC or 6H—SiC substrate, in particular, a substrate having a (0001) plane is in wide use. To form a SiC thin film on the substrate by performing an epitaxial growth process, an inclined substrate from the (0001) plane as the standard plane, for example, a substrate tilted toward the [11-20] axis by 8°, in the case of a 4H—SiC substrate is commonly used, whereby a step-terrace pattern is formed on the surface of the SiC substrate.
For example, a method of forming a step-terrace structure by keeping a 4H—SiC substrate in an HCl (0 to 0.1%)-added H2 atmosphere at 1,430° C. for 15 to 30 minutes has been disclosed (see, for example, H. Nakagawa et al., PRL91 (2003) 226107-1-4).
In connection with the above method, a method of depositing a SiC thin film on a SiC bulk substrate by supplying a gas containing nitrogen intermittently after supplying material gases which contain Si and C has also been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-234301).
It is essential that the SiC film can be formed by epitaxial growth on the stepwise pattern of the step-terrace structure to produce devices using the step-terrace structure such as quantum wire devices, optical devices and electronic devices. However, in conventional techniques, the stepwise pattern is formed on the substrate surface at a temperature of 1,430° C., which is below the favorable range for a 4H—SiC to grow epitaxially, and hence the stepwise pattern cannot retain its structure due to deformation caused by the increase of temperature.
Furthermore, the above-mentioned method of depositing a SiC thin film by intermittently supplying a nitrogen-containing gas is not intended for forming a stepwise pattern on the substrate surface, but for eliminating the stepwise pattern to smooth the substrate surface by performing epitaxial growth when a SiC thin film is grown on the above-mentioned substrate having an off angle.
Thus, the method of forming a desirable stepwise pattern, in particular a stepwise pattern exhibiting favorable periodicity, e.g. a periodic stepwise pattern having a terrace width of 40 nm or more and a step height of 5 nm or more, on the surface of a SiC substrate is yet to be established.